1. Field of the Invention
The present invention is directed to an ultrasonic flow meter of the type for determining a flow in a measurement channel, having a first sensor chamber with a first membrane disposed against the measurement channel and a first transducer disposed at a specific distance from the first membrane, and a second sensor chamber with a second membrane disposed against the measurement channel and a second transducer disposed at a specific distance from the second membrane, with the first and second membranes being gas-tight.
2. Description of the Prior Art
Ultrasonic flow meters are known in various areas of flow measurement, including the medical field in which the flow of gas expired by a patient is measured. The technique is well known and employs transducers that transmit sound waves between each other, with the transit time measured upstream and downstream serving as the basis for calculating the flow.
When a measurement is to be made in a sensitive environment or, in the case of medical applications, when contamination of the transducers must be avoided, a membrane is utilized between the transducers and the measurement channel.
These membranes can consist of porous filters with a bacteria-blocking capability, however, porous filters with a sufficient bacteria-blocking effect are too thick and have a damping effect on ultrasound. The membrane can instead be gas-tight for reliable prevention of contamination.
The membrane should also be as thin as possible, preferably less than 10 xcexcm, in order to pass ultrasonic waves as effectively as possible. For such thin membranes, variations in pressure that could cause the membrane to rupture are then a risk.
Ideally, therefore, the membrane should be durable enough to withstand extended usage and resist rupturing.
An object of the present invention is to provide an ultrasonic flow meter that avoids the aforesaid problems.
The above object is achieved in accordance with the invention in an ultrasonic flow meter of the type initially described, wherein the first and second sensor chambers each are gas-tight, and wherein a first gas line connects the first sensor chamber to the measurement channel and a second gas line connects the second sensor chamber to the measurement channel.
Another object of the invention is to provide a ventilator in which the ultrasonic flow meter is incorporated.
This object is achieved in accordance with the invention in a ventilator which supplies a breathing gas to a patient via a gas line in which an ultrasonic flow meter is disposed for measuring the flow of the breathing gas, the ultrasonic flow meter being constructed in accordance with the invention as described immediately above.
When the sensor chambers are connected to the measurement channel, pressure equalization is achieved that minimizes the loading to which the membrane is subjected, and membranes can accordingly be made as thin as possible.
Filters should be arranged by the connections between the measurement channel and the sensor chambers in order to prevent contamination.